It is known that a vast amount of energy is contained in the latent heat of vaporization of water vapor in humid air.
In U.S. Pat. No. 3,894,393 (Carlson) a method and means for the generation of power from a controlled air flow was disclosed. An enclosed air mass is cooled at high altitude, below the temperature of the surrounding air. This is done by spraying water, optionally pumped from the sea to the top of a large duct, into the air, at the desired altitude. The treated air is isolated from the surrounding air by means of a large duct. The resulting cooler, denser air flows down the duct toward lower altitude, and the energy of the falling air mass is extracted by means of a turbine generator. It was stated that the net power output of the system is the gross power available from the turbine minus the power to pump the water and the power loss in duct drag and emerging air kinetic energy.
Research was conducted in the late seventies by T. K. Oliver and others (Energy from Humid Air, T. K. Oliver et al., J. Energy, Vol. 2, No. 1, January-February 1978, p. 63), primarily by computer modeling, to investigate the concept of converting the energy in humid air into mechanical work (i.e. to drive an electrical generator). It was stated in the aforementioned research that the proposed process is to be thought of as a heat engine with the air itself acting as the working fluid.
The idea of processing the humid air in order to recover the latent heat of vaporization is attractive considering the following standpoints (as stated in the research). The energy of the sun is virtually limitless, and it is known that some 35% of the solar energy that reaches the Earth's surface is used to evaporate water. The collector of the solar energy exists in nature in the form of oceans or tropical rain forests. With any reasonable air circulation the system will operate as an energy conversion plant. Fresh water is obtained as a by-product in the process.
The research put forward some preliminary stipulations. First, the humid air itself is to be the working fluid (of the heat engine), and second, the process has to be of continuous-flow with the air passing through ducts and turbines, as necessary. It was argued that it will not be possible to attain high efficiency in converting latent heat of vaporization into useful work, however this was not the important consideration since humid air is free and plentiful. On the other hand, a most important consideration was the energy output compared to unit of plant investment and operating cost. If this proved favorable then a low conversion efficiency would be tolerable. The proposed process of humid air power generation in the research was called "Natural Draft Tower". It was described as a vertical, natural draft, condensation tower. The efficiency of such a tower was claimed to be dependent upon the degree of saturation of the ambient air at the upper inlet, upon the tower height and upon the prevailing atmospheric temperature lapse rate.
Carlson's invention was the basis for Prof. Dan Zaslavsky's proposed SNAP (SNeh Areo-electric Power) project (Zaslavsky D. (1995) "SNAP Technology--A major source of low cost electric power and desalinated water", Technion-Israel Institute of Technology). In the SNAP project it was proposed to erect power plants in desert areas for the generation of electric power with the method described by Carlson, using sea water, and obtaining desalinated water, as a by-product.
In U.S. Pat. No. 4,801,811 (Assaf et al.) it was described a method and a system for generating electricity in an arid environment. Electricity is generated using an open duct such as a canyon that is closed at one end, and open at the other by erecting an air dam at the open end of the canyon, and locating an air turbogenerator in the base of the dam. The air in the canyon is cooled by spraying water into the air as it enters the canyon. The cooled air then flows downwardly toward the base of the dam and through the turbogenerator. The air dam described by Assaf consisted a flexible curtain, suspended at its top by suspension means like a cable suspended between towers erected on both sides of the canyon's open end.
However, the method described by Oliver, Carlson's invention, Assaf's invention and the proposed SNAP project all seem to have some serious drawbacks. First, with the exception of Assaf's invention, they all require the existence of an extremely high tower or duct, with a very large diameter. The proposed tower height is in the order of a thousand (or even several thousand) meters. Its proposed diameter is in the order of hundred, or several hundred, meters. Such a tower has never been built before. This inevitably involves complex engineering considerations and problems, and heavy erection costs. Second, sea water transportation to desert or other inland locations requires the establishment of a system of water pipes and pumping stations along the pipes, and this too is very costly.
Assaf's invention on the other hand, required the existence of a canyon and the erection of an air dam at the open end of a canyon. It is argued that canyons that would suite Assaf's requirements are not widely available, and furthermore the erection of an air dam according to Assaf's invention is in itself a costly engineering challenge. It should be noted that a canyon suitable for such an operation is to be relatively steep if it is to effectively serve its purpose.
Another drawback is the creation of vast amounts of salt which constitutes an environmental hazard to the soil, and this is why such power plants are preferably located in remote isolated desert locations. Such a location increases water transportation costs, and subsequently, also increases the costs of long power lines, supplying the generated electricity to the consumers.
It is the object of the present invention to provide a method and means for the generation of power from humid air which is cheaper and more practical than the methods and means described in the prior art.
Another object of the present invention is to provide a method and means for the generation of power from humid air which does not require the erection of an air tower or the employment of a duct.